A continuous steel caster is a machine that transforms or casts molten steel into solidified semi-finished shapes such as billets, blooms, and slabs. Specifically, molten steel from a steelmaking furnace, usually a basic oxygen furnace, is poured into a trough-shaped container called a tundish. The tundish is placed over a device which sizes and shapes the steel known as the caster mold. Steel from the tundish is poured into the mold through an an apparatus known as a tundish shroud. As the molten steel flows out of the mold, the steel takes the form of a strand and is moved through cooling devices by an array of motorized rollers. Thus, a continuous supply of molten steel to the caster will allow steel to be cast without interruption. Many continuous casters are constructed with multiple molds so that several strands of steel can be cast simultaneously.
Manufacturing requirements often mandate that several grades of steel, that is, steels having different metallurgical properties, be continuously cast. Usually, when a different grade of steel is to be cast, the caster must be emptied of the steel previously cast before the different grade of steel can be poured. This creates an interruption in the casting process resulting in a loss of production time.
In an attempt to eliminate the loss of down time incurred between the casting of different grades of steel in a continuous casting process, efforts have been made to sequentially cast such different grades of steel. Sequential casting, however, usually lowers the yield of marketable steel because the mixing of the two different grades of steel in and below the caster mold creates a lengthy transition zone of chemically non-uniform material. Recent efforts to minimize the amount of mixing between two grades of steel have resulted in the use of various types of metallic devices commonly called grade separators which, when inserted into a mold filled with molten steel, act as cooling devices and precipitate the formation of a solidified barrier between the two grades of molten steel. Such devices have been disclosed in U.S. Pat. No. 4,250,945 and U.S. Pat. No. 4,269,257. This solidified barrier greatly reduces the amount of mixing between the two different grades of steel while eliminating much of the down time previously incurred when casting different grades of steel without grade separators.
A problem that arises, however, from the use of grade separating devices is the potential safety hazards encountered when inserting such devices into a caster mold. Although the grade separators can be inserted manually, safety regulations and requirements often prohibit manual insertion. Furthermore, manual insertion creates a timing problem. The grade separator should be inserted during the time a tundish is replaced with another tundish containing a different grade of steel and prior to any solidification in the caster mold of the horizontal end surface of the molten steel strand. If a continuous caster is constructed to cast multiple strands of steel simultaneously, the amount of time necessary to manually insert several grade separators into the caster mold will prohibit the completion of the insertion procedure during the time tundishes are being changed unless additional labor is used. Without such additional labor, the casting process would be delayed until the insertion procedure is completed. Thus, both safety and time considerations mandate that grade separators be inserted by non-manual methods.